Fuse status indicators have long been known including fuse status indicators for multi-phase electrical systems commonly used to power heavy equipment in industrial applications. Often such indicators utilized a neon lamp or other lamp associated with each fuse which would illuminate when the fuse was blown or other malfunction failed to provide an electrical connection for one of the lines of the three-phase or multi-phase system to the load.
Frequently, such prior fuse status indicators included one or more push button switches for testing the indicator light; otherwise there might be a blown fuse or other fault which would go undetected. Recently, more complicated fuse status indicator circuits utilizing LED indicator lights rather than neon lamps have been employed but they also have generally produced only a "fuse bad" indication and if the fuse status indicator itself was defective then a blown fuse or other fault might go undetected.
Examples of such prior fuse status indicator circuits are shown in U.S. Pat. No. 4,857,896 to Brooks, dated Aug. 15, 1989; U.S. Pat. No. 5,343,192 to Yenisey, dated Aug. 30, 1994; and Statutory Registration No. H248 to Middlebrooks, published Apr. 7, 1987.
Other low voltage electrical systems have sought to provide fuse status indicators for multiple DC loads and their associated fuses which would indicate a particular blown fuse or other fault by failure of the associated LED to be illuminated upon closing a test switch. Such a system is shown in U.S. Pat. No. 4,281,322 to Nasu et al., issued Jul. 28, 1981. This circuit is clearly not adaptable for use in a high-voltage AC multi-phase power system.